documentclass{standalone}

usepackage{tcolorbox}
usepackage{multicol}

newtcolorbox{objbox}[1] {colback=red!5!white,colframe=red!75!black,fonttitle=bfseries,title=#1, before skip=0.5cm, after skip=0.5cm}  %

newenvironment{objectives}{%
    begin{objbox}{Objectives:} begin{list}{(bullet)}{}%
}{%
    end{list} end{objbox}%
}%

begin{document}

begin{objectives}
    item foo:
    begin{multicols}{2}
        item one
        item two
    end{multicols}
end{objectives}

end{document}

documentclass{article}
usepackage{enumitem}
usepackage{tasks}
usepackage{tcolorbox}
usepackage{multicol}
usepackage{shortlst, setspace}
newenvironment{boxeditemize}[1][3]{settowidth{labelwidth}{mbox{textbullet}}%
setlength{leftmargini}{dimexprlabelwidth+labelseprelax}%
setlength{shortitemwidth}{dimexprlinewidth/#1-labelwidth-2labelseprelax}%
begin{shortitemize}}%{1.333}
{end{shortitemize}}%
%%
newtcolorbox{objbox}[1] {colback=red!5!white,colframe=red!75!black,fonttitle=bfseries,title=#1, before skip=0.5cm, after skip=0.5cm} %

newenvironment{myobjectives}{%
    begin{objbox}{Objectives: (with texttt{enumitem})} begin{itemize}[wide=0pt, leftmargin =*]%
}{%
    end{itemize} end{objbox}%
}%

newenvironment{otherobjectives}[1][3]{%
 begin{objbox}{Objectives (with texttt{shortlst})}%
begin{boxeditemize}[#1]
}{%
 end{boxeditemize} end{objbox}%
}%

newcommandparitem[2][1]{item parbox[t]{#1shortitemwidth}{#2medskip}}

begin{document}

begin{myobjectives}
 item foo:
  begin{multicols}{2}
 item one
 item two
 end{multicols}
end{myobjectives}

par
begin{objbox}{Objectives: (with texttt{tasks})}settasks{style = itemize, item-indent = 0em, label-offset =-0.2em, before-skip = -1.5ex, after-skip =-3ex}%
begin{tasks}(2)
 task* foo:
 task one
 task two
 end{tasks}
end{objbox}

begin{otherobjectives}[2]setstretch{2.5}
 item foo:
 item one
 item two
end{otherobjectives}

begin{otherobjectives}[2]
 item foo;
 paritem[2] {Bla bla bla bla bla. Bla bla bla bla bla. Bla bla bla bla bla. Bla bla bla bla bla. }
 paritem{Bli bli bli bli bli. Bli bli bli bli bli. Bli bli bli bli bli. Bli bli bli bli bli. Bli bli bli bli bli. }
 item one
 item two
end{otherobjectives}

end{document}

documentclass{standalone}

usepackage{tcolorbox}
usepackage{multicol}

newtcolorbox{objbox}[1] {colback=red!5!white,colframe=red!75!black,fonttitle=bfseries,title=#1, before skip=0.5cm, after skip=0.5cm}  %

newenvironment{objectives}{%
    begin{objbox}{Objectives:} begin{list}{(bullet)}{}%
}{%
    end{list} end{objbox}%
}%

begin{document}

begin{objectives}
    item foo: % empty line below this is important

    parbox{5cm}{
        begin{multicols}{2}
            item one
            item two
        end{multicols}
    }
end{objectives}

end{document}